1. Field of the Invention
The present invention relates generally to an artificial flame device that produces a visual effect similar to a real candle flame.
2. Background
Simulated battery powered flameless candles have been popular in recent years, and much work has been undertaken to advance the state of the technology.
Typical early simulated candles used simple electric screw-in lamps, which provided a static though bright simulation of a flame. A variety of lamps have been created which are designed to mimic the shape of a flame. Because there was no flicker, and also because of their typically large size, these were limited in their ability to create a realistic flame effect.
A major breakthrough in nameless candle technology came with U.S. Pat. No. 6,616,308, which eliminated the whole concept of an exposed simulated flame structure that is directly visible, which is hard to make look realistic. Instead in this approach the simulated wax candle is lit internally as if the flame had burned down within the candle wax. This approach has been very popular and is widely sold today.
However, there has always been a need for a more realistic visible simulated flame structure. Some candles, particularly narrow ones like tapers are not conducive to the hidden flame approach and through the years various approaches have been taken to attempt to create a more realistic flame structure.
U.S. Pat. No. 4,551,794 discloses an imitation flame that uses an incandescent light source, but improves the flame simulation, by positioning the flame on the top of a moving pendulum which is driven by an electromagnetic system that allows the flame to wiggle, or move from side to side. This gives the impression from certain viewing angles of a flame that is moved from side-to-side by a gentle breeze. This can provide a good side-to-side sense of motion but it does not provide any sense of vertical movement of the flame. While this approach was a major improvement over static flames, there are a number of disadvantages with this approach. From a manufacturing standpoint this approach is expensive to build because it requires many moving parts with moving electrical connection points through the pivoting axis to power the lit flame. These moving structures are also fragile and subject to damage in handling and shipment. Another challenge is the power consumption of the magnetic drive mechanism is significant, requiring additional power that would otherwise be available to light the flame, thereby reducing battery life and limiting application to those with steady AC power available through house wiring.
An improvement to the pendulum flame approach is found in U.S. Pat. No. 7,837,355. With this approach the cumbersome routing of power to the flame is eliminated by positioning a light source below the flame and projecting light onto a flat flame-shaped projection surface that is also moved by a pendulum driven by an electromagnet. In some cases as implemented by manufacturers, the flame projection surface has a loose fit on is axis of rotation thus allowing some modest rotation about a second axis. This allows not only forward and backward motion of the flame, but also some side-to-side motion which enhances the flame simulation over a somewhat wider viewing angle. Because the flame is lighter weight it has advantages in terms of the power consumption required by the electromagnetic drive system which can be much lighter duty than earlier incandescent products. However this approach still must allocate a significant amount of power to the electromagnetic drive mechanism reducing battery life and which also has significant cost involved in the electromagnetic drive coil. Because the flame-shaped surface onto which the LEDs project is relatively two dimensional, and because the candle is driven by directional LEDs typically on one side only, the candle flame is only effectively viewed over a field of view of less than 180 degrees. As in other approaches, this is successful in creating the effect of side-to-side flame movement, but not the more up-and-down movement seen in a flame that is affected by a gentle breeze.
Another way to create an improved flame effect without moving parts is found in U.S. Pat. No. 5,924,784 which describes a simulated flame that uses a plurality of small LEDs contained on a circuit board within a flame-shaped bulb. The LEDs can also be a variety of colors and the intent is to provide individual microprocessor control of these LEDs in a way that can simulate the flickering of a flame. This approach has a number of challenges, one is the high cost of the large number of LEDs required and also the development of a sequencing pattern of the LEDs that is effective in producing a realistic flicker. Another is the challenge of effectively diffusing the light sources so that they do not appear as separate point sources of light. Because of the relatively directional nature of the LEDs, it is hard to attain even illumination over a wide range of viewing angles of the flame with a diffusing structure, and this approach could work for a flame that might be viewed from front or back, but may be less effective when viewed from the side. As with other approaches, there is no mention of a method that will yield a flame simulation that has an effective up-and-down motion.
Similarly, U.S. Pat. No. 4,510,556 discloses a candle flame more simply composed of 3 light sources in a stacked arrangement within a flame structure. To simulate the turbulence of a flame they alter the duty cycle of the power to each light source, with the lowest source being the brightest with a relatively small flicker, with the middle source being less bright, and with a higher level of flicker, and then the uppermost LED being the most dim, at about half the brightness level of the lowest LED, and with a greater flicker. This creates a flame with decreasing brightness to the top, and with a stated clock frequency of 40 Hz, provides a relatively rapid pulse or flickering pattern that is at a level just perceptible to the eye. This effect could be accurately described as more of a shimmering effect as opposed to the more aggressive high frequency flickers found on products typically in the market today. However this will not produce any up-and-down sense movement of the flame, thus limiting its simulation effectiveness.
Another more recent variation in this approach is found in U.S. Pat. No. 6,926,423, which also seeks to simulate the appearance of a gas flame, such as what might be typically found in a gas lantern. Like the earlier patent they recognize the importance in a stacked arrangement of LEDs to have the lowest LED the brightest and the highest LED much dimmer, as might be found in a tapered flame. This also discloses a flicker or oscillation in the upper two LEDs that are independent of one another, but with a lower LED that does not flicker. This provides a continuous level of light from the bottom of the flame, with light above that providing variable oscillation or flicker, thus simulating a flame. White this produces a random flickering effect, it does not disclose how to create an effective up-and-down motion of the flame.
What is missing from all of these approaches is a simple, low-cost approach to simulate a flame which can create a clear sense of deliberate motion in an upward and downward direction, which can be viewed from any angle, and which can also achieve superior battery life performance.